Abstract: A system and method are provided for controlling a three-phase pulse-width-modulated alternating-current voltage regulator, in order to reduce inrush current when starting, for example, a large three-phase induction motor. The system and method include a set of four-quadrant switches connected in a converter circuit between the input voltage and the output load. By applying certain switching states in a determined sequence based on sensed values of the input voltage at the three lines, the system and method synthesize a three-phase variable magnitude output voltage from the three-phase input voltage of fixed magnitude.

Abstract: A method is provided for implementing a three-phase pulse-width-modulated alternating current voltage regulator including six four-quadrant switches, wherein each four-quadrant switch includes two two-quadrant switches. Three series branches, each series branch including one four-quadrant switch, and three shunt branches, each shunt branch including one four-quadrant switch, are provided. To obtain a desired converter state, the two-quadrant switches in the series and shunt branches are turned on or off in a predetermined sequence.

Abstract: A method or system consistent with this invention for detecting if a thyristor failed open in an alternating current input phase of a load comprises measuring an instantaneous power delivered to the load during a cycle of the input; determining a peak power delivered to the load during the cycle of the input; calculating an average power delivered to the load during the cycle of the input; and determining if the thyristor failed open by comparing the magnitudes of the peak power and the average power.

Abstract: Methods and systems consistent with this invention detect a failed short thyristor in a solid-state controller for delivering power to a load during reduced-voltage operation. Methods and systems consistent with this invention detect a voltage across the thyristor, and indicate a failed short thyristor when the absolute value of the voltage across the thyristor remains below a threshold value during a predetermined period of time. Methods and systems consistent with this invention detect a failed open thyristor in a solid-state controller during full-voltage operation. Methods and systems consistent with this invention detect a voltage across the thyristor, and indicate a failed open thyristor when the absolute value of the voltage across the thyristor exceeds a threshold value.